JP5152415B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

The engine exhaust passage, NO _X storage catalyst air-fuel ratio of the inflowing exhaust gas when the lean that releases NO _X air-fuel ratio of the exhaust gas which is occluded becomes rich for occluding NO _X contained in the exhaust gas inflow was placed, NO _X occluding catalyst upstream of the engine oxidation catalyst having an adsorbing function in the exhaust passage disposed, NO _X from occluding catalyst when releasing the NO _X is feeding hydrocarbons into the engine exhaust passage an oxidation catalyst upstream An internal combustion engine in which the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is made rich is known (see, for example, Patent Document 1).
In this internal combustion engine, hydrocarbons supplied when NO _X is to be released from the NO _X storage catalyst are converted into gaseous hydrocarbons in the oxidation catalyst, and the gaseous hydrocarbons are sent to the NO _X storage catalyst. As a result, the NO _X released from the NO _X storing catalyst is made to satisfactorily reduced.

Patent No. 3969450

However, the NO _X storage catalyst has a problem that the NO _X purification rate decreases when the temperature becomes high.
An object of the present invention is to provide an exhaust purification device for an internal combustion engine that can obtain a high NO _x purification rate even when the temperature of the exhaust purification catalyst becomes high while selectively using two types of hydrocarbon supply methods. It is in.

According to the present invention, the hydrocarbon supply valve for supplying hydrocarbons is disposed in the engine exhaust passage, and the hydrocarbon and exhaust gas injected from the hydrocarbon supply valve into the engine exhaust passage downstream of the hydrocarbon supply valve An exhaust purification catalyst for reacting with NO _X contained therein is arranged, a noble metal catalyst is supported on the exhaust gas flow surface of the exhaust purification catalyst, and a basic exhaust gas flow surface around the noble metal catalyst The exhaust purification catalyst is injected into the exhaust gas when the hydrocarbon is injected from the hydrocarbon supply valve at a predetermined supply interval so that the air-fuel ratio of the exhaust gas decreases to a predetermined air-fuel ratio. which has a property for reducing the NO _X contained, your storage amount of the NO _X contained in the exhaust gas to be longer than the predetermined supply interval supply interval of hydrocarbons have the property of increasing , NO which the air-fuel ratio of the exhaust gas hydrocarbons from the hydrocarbon feed valve at the time of engine operation includes injection to the exhaust gas at a predetermined feed distance above to decrease until the air-fuel ratio predetermined described above First hydrocarbon supply method for purifying _X and fuel necessary for reducing the amount of hydrocarbons supplied from the hydrocarbon supply valve and reducing the air-fuel ratio of the exhaust gas to the aforementioned predetermined air-fuel ratio An exhaust gas purification apparatus for an internal combustion engine is provided that selectively uses the second hydrocarbon supply method for supplying gas into the combustion chamber during the latter half of the expansion stroke or during the exhaust stroke.

A high NO _x purification rate can be obtained even when the temperature of the exhaust purification catalyst becomes high while selectively using the first hydrocarbon supply method and the second hydrocarbon supply method.

FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 is a view schematically showing the surface portion of the catalyst carrier.
FIG. 3 is a view for explaining an oxidation reaction in the exhaust purification catalyst.
FIG. 4 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
Figure 5 is a diagram illustrating a NO _X purification rate.
6A and 6B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
7A and 7B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
FIG. 8 is a diagram showing a change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
Figure 9 is a diagram illustrating a NO _X purification rate.
FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 12 is a diagram showing the relationship between the oxidizing power of the exhaust purification catalyst and the required minimum air-fuel ratio X.
FIG. 13 is a graph showing the relationship between the oxygen concentration in the exhaust gas and the amplitude ΔH of the hydrocarbon concentration, with which the same NO _x purification rate can be obtained.
Figure 14 is a diagram showing a relationship between an amplitude ΔH and NO _X purification rate of hydrocarbon concentration.
Figure 15 is a diagram showing the relationship between the vibration period ΔT and NO _X purification rate of hydrocarbon concentration.
16A, 16B, and 16C are diagrams showing a map of the hydrocarbon feed amount W and the like.
FIG. 17 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
Figure 18 is a diagram illustrating a map of exhaust amount of NO _X NOXA.
FIG. 19 shows the fuel injection timing.
FIG. 20 is a diagram showing a map of the hydrocarbon supply amount WR.
21A and 21B are views for explaining the first hydrocarbon supply method and the second hydrocarbon supply method.
22A, 22B, and 22C are views showing the hydrocarbon feed amount WA and the like.
FIG. 23 is a time chart showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
FIG. 24 is a time chart showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
25A and 25B are time charts showing the temperature rise control.
FIG. 26 is a diagram showing the NO _X purification rate and the NO _X storage rate.
FIG. 27 is a flowchart for detecting the minimum air-fuel ratio.
28 and 29 are flowcharts for performing operation control.
FIG. 30 is a flowchart showing the interrupt routine.
FIG. 31 is a flowchart showing an interrupt routine.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.
On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7b is connected to the inlet of the exhaust purification catalyst 13 via the exhaust pipe 12, and the outlet of the exhaust purification catalyst 13 is connected to the particulate filter 14 for collecting particulates contained in the exhaust gas. . In the exhaust pipe 12 upstream of the exhaust purification catalyst 13, a hydrocarbon supply valve 15 for supplying hydrocarbons composed of light oil and other fuels used as fuel for the compression ignition internal combustion engine is disposed. In the embodiment shown in FIG. 1, light oil is used as the hydrocarbon supplied from the hydrocarbon supply valve 15. The present invention can also be applied to a spark ignition type internal combustion engine in which combustion is performed under a lean air-fuel ratio. In this case, the hydrocarbon supply valve 15 supplies hydrocarbons made of gasoline or other fuel used as fuel for the spark ignition internal combustion engine.
On the other hand, the exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 16, and an electronically controlled EGR control valve 17 is disposed in the EGR passage 16. A cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 20 via a fuel supply pipe 19, and this common rail 20 is connected to a fuel tank 22 via an electronically controlled fuel pump 21 having a variable discharge amount. The fuel stored in the fuel tank 22 is supplied into the common rail 20 by the fuel pump 21, and the fuel supplied into the common rail 20 is supplied to the fuel injection valve 3 through each fuel supply pipe 19.
The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. A temperature sensor 23 for detecting the temperature of the exhaust purification catalyst 13 is attached downstream of the exhaust purification catalyst 13, and the differential pressure for detecting the differential pressure before and after the particulate filter 14 is attached to the particulate filter 14. A sensor 24 is attached. Further, a temperature sensor 25 for detecting the temperature of the particulate filter 14 is disposed downstream of the particulate filter 14, and an air-fuel ratio sensor 26 is disposed in the exhaust pipe 12 downstream of the hydrocarbon supply valve 15. Has been. The output signals of the temperature sensors 23 and 25, the differential pressure sensor 24, the air-fuel ratio sensor 26, and the intake air amount detector 8 are input to the input port 35 via corresponding AD converters 37, respectively. A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the hydrocarbon supply valve 15, the EGR control valve 17, and the fuel pump 21 through corresponding drive circuits 38.
FIG. 2 schematically shows the surface portion of the catalyst carrier carried on the substrate of the exhaust purification catalyst 13. In this exhaust purification catalyst 13, as shown in FIG. 2, noble metal catalysts 51 and 52 are supported on a catalyst support 50 made of alumina, for example, and further on this catalyst support 50 potassium K, sodium Na, cesium Cs. selected from an alkali metal, barium Ba, alkaline earth metals such as calcium Ca, rare earth and silver Ag, such as lanthanides, copper Cu, iron Fe, the metal capable of donating an electron to the NO _X such as iridium Ir, such as A basic layer 53 containing at least one of them is formed. Since the exhaust gas flows along the catalyst carrier 50, it can be said that the noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13. Further, since the surface of the basic layer 53 is basic, the surface of the basic layer 53 is referred to as a basic exhaust gas flow surface portion 54.
On the other hand, in FIG. 2, the noble metal catalyst 51 is made of platinum Pt, and the noble metal catalyst 52 is made of rhodium Rh. That is, the noble metal catalysts 51 and 52 carried on the catalyst carrier 50 are composed of platinum Pt and rhodium Rh. In addition to platinum Pt and rhodium Rh, palladium Pd can be further supported on the catalyst carrier 50 of the exhaust purification catalyst 13, or palladium Pd can be supported instead of rhodium Rh. That is, the noble metal catalysts 51 and 52 supported on the catalyst carrier 50 are composed of platinum Pt and at least one of rhodium Rh and palladium Pd.
When hydrocarbons are injected into the exhaust gas from the hydrocarbon supply valve 15, the hydrocarbons are reformed in the exhaust purification catalyst 13. In the present invention, so as to purify the NO _X in the exhaust purification catalyst 13 using the time reformed hydrocarbons. FIG. 3 schematically shows the reforming action performed in the exhaust purification catalyst 13 at this time. As shown in FIG. 3, the hydrocarbon HC injected from the hydrocarbon feed valve 15 is converted into a radical hydrocarbon HC having a small number of carbons by the catalyst 51.
FIG. 4 shows the supply timing of hydrocarbons from the hydrocarbon supply valve 15 and changes in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13. Since the change in the air-fuel ratio (A / F) in depends on the change in the concentration of hydrocarbons in the exhaust gas flowing into the exhaust purification catalyst 13, the air-fuel ratio (A / F) in shown in FIG. It can be said that the change represents a change in hydrocarbon concentration. However, since the air-fuel ratio (A / F) in decreases as the hydrocarbon concentration increases, the hydrocarbon concentration increases as the air-fuel ratio (A / F) in becomes richer in FIG.
FIG. 5 shows exhaust purification as shown in FIG. 4 by periodically supplying hydrocarbons from the hydrocarbon supply valve 15, that is, by periodically changing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13. shows the NO _X purification rate by the exhaust purification catalyst 13 when changing the air-fuel ratio (a / F) in of the exhaust gas flowing into the catalyst 13 for each catalyst temperature TC of the exhaust purification catalyst 13. The inventor has conducted research on NO _X purification over a long period of time, and in the course of the research, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is set to an amplitude within a predetermined range and a predetermined range. FIG. 5 shows that when the fuel is vibrated with the internal period, that is, when the hydrocarbon is injected from the hydrocarbon supply valve 15 at a predetermined supply interval so that the air-fuel ratio of the exhaust gas decreases to a predetermined air-fuel ratio. As shown, it has been found that an extremely high NO _x purification rate can be obtained even in a high temperature region of 400 ° C. or higher.
Further, at this time, a large amount of the reducing intermediate containing nitrogen and hydrocarbon continues to be held or adsorbed on the surface of the basic layer 53, that is, on the basic exhaust gas flow surface portion 54 of the exhaust purification catalyst 13. it is of has been found that reducing intermediate plays a central role in obtaining a high NO _X purification rate. Next, this will be described with reference to FIGS. 6A and 6B. 6A and 6B schematically show the surface portion of the catalyst carrier 50 of the exhaust purification catalyst 13, and in these FIGS. 6A and 6B, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is predetermined. When the vibration is vibrated with the amplitude within the range and the period within the predetermined range, that is, the hydrocarbon is removed from the hydrocarbon supply valve 15 in advance so that the air-fuel ratio of the exhaust gas is lowered to the predetermined air-fuel ratio. The reaction presumed to occur when spraying at a defined supply interval is shown.
FIG. 6A shows a case where the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is low, and FIG. 6B shows that the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 when hydrocarbons are supplied from the hydrocarbon supply valve 15 is high. It shows when
As can be seen from FIG. 4, since the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 is maintained lean except for a moment, the exhaust gas flowing into the exhaust purification catalyst 13 is usually in an oxygen excess state. Therefore, as shown in FIG. 6A, NO contained in the exhaust gas is oxidized on the platinum 51 to become NO ₂ , and then this NO ₂ is donated with electrons from the platinum 51 to become NO ₂ ⁻ . Accordingly, a large amount of NO ₂ ⁻ is generated on the platinum 51. The NO ₂ ^- is strongly active, or the NO ₂ ^- is referred to as the active _NO ^{2 *.}
On the other hand, when hydrocarbons are supplied from the hydrocarbon supply valve 15, as shown in FIG. 3, the hydrocarbons are reformed in the exhaust purification catalyst 13 and become radicals. As a result, as shown in FIG. 6B, the hydrocarbon concentration around the active NO ₂ ^* increases. By the way, after active NO ₂ ^* is generated, when a state in which the oxygen concentration around the active NO ₂ ^* is high continues for a certain period of time, the active NO ₂ ^* is oxidized and enters the basic layer 53 in the form of nitrate ions NO ₃ ^−. Absorbed. However react with radical hydrocarbons HC in the active NO ₂ ^* around the hydrocarbon concentration is high is being when the active NO ₂ ^* platinum 51 as shown in Figure 6B before the lapse of this period of time, whereby A reducing intermediate is produced. This reducing intermediate is attached or adsorbed on the surface of the basic layer 53.
Incidentally, the first produced reducing intermediate this time is considered to be a nitro compound R-NO _2. When this nitro compound R-NO ₂ is produced, it becomes a nitrile compound R-CN, but since this nitrile compound R-CN can only survive for a moment in that state, it immediately becomes an isocyanate compound R-NCO. This isocyanate compound R—NCO becomes an amine compound R—NH _{2 when} hydrolyzed. However, in this case, it is considered that a part of the isocyanate compound R-NCO is hydrolyzed. Therefore, as shown in FIG. 6B, most of the reducing intermediates retained or adsorbed on the surface of the basic layer 53 are considered to be the isocyanate compound R—NCO and the amine compound R—NH ₂ .
On the other hand, as shown in FIG. 6B, when hydrocarbon HC surrounds the generated reducing intermediate, the reducing intermediate is blocked by hydrocarbon HC and the reaction does not proceed further. In this case, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is lowered, and as a result, when the oxygen concentration is increased, the hydrocarbons around the reducing intermediate are oxidized. As a result, as shown in FIG. 6A, the reducing intermediate and active NO ₂ ^* react. At this time, the active NO ₂ ^* reacts with the reducing intermediates R—NCO and R—NH ₂ to become N ₂ , CO ₂ , H ₂ O, and thus NO _X is purified.
In this way, in the exhaust purification catalyst 13, a reducing intermediate is generated by increasing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13, and the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is decreased to reduce the oxygen concentration. By increasing the NO, active NO ₂ ^* reacts with the reducing intermediate, and NO _X is purified. That is, in order to purify the NO _X by the exhaust purification catalyst 13, it is necessary to change the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 periodically.
Of course, in this case, the hydrocarbon concentration needs to be increased to a concentration high enough to produce a reducing intermediate, and carbonized to a concentration low enough to react the resulting reducing intermediate with active NO ₂ ^*. It is necessary to reduce the concentration of hydrogen. That is, it is necessary to vibrate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with an amplitude within a predetermined range. In this case, a sufficient amount of the reducing intermediate R-NCO or R-NH ₂ is put on the basic layer 53, that is, basic exhaust gas, until the generated reducing intermediate reacts with active NO ₂ ^*. A basic exhaust gas flow surface portion 24 is provided for this purpose, which must be retained on the gas flow surface portion 24.
On the other hand, if the supply cycle of the hydrocarbon is lengthened, the period during which the oxygen concentration becomes high after the hydrocarbon is supplied and before the next hydrocarbon is supplied becomes longer, so that the active NO ₂ ^* is reduced to the reducing intermediate. Without being generated in the basic layer 53 in the form of nitrate. In order to avoid this, it is necessary to oscillate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with a period within a predetermined range.
Therefore, in the embodiment according to the present invention, NO _X contained in the exhaust gas is reacted with the reformed hydrocarbon to produce reducing intermediates R-NCO and R-NH ₂ containing nitrogen and hydrocarbons. Further, noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13, and the generated reducing intermediates R-NCO and R-NH ₂ are held in the exhaust purification catalyst 13. Therefore, a basic exhaust gas flow surface portion 54 is formed around the noble metal catalysts 51 and 52, and the reducing intermediates R-NCO and R-NH held on the basic exhaust gas flow surface portion 54 are formed. NO _X is reduced by the _second reduction action, the vibration period of the hydrocarbon concentration, i.e. to feed period of hydrocarbons from the hydrocarbon feed valve 15 continues to generate the reducing intermediate R-NCO or R-NH ₂ The required period. Incidentally, in the example shown in FIG. 4, the injection interval is 3 seconds.
When the oscillation period of the hydrocarbon concentration, that is, the supply period of the hydrocarbon HC is longer than the period within the above-described predetermined range, the reducing intermediates R-NCO and R-NH ₂ are formed from the surface of the basic layer 53. At this time, the active NO ₂ ^* produced on the platinum Pt 53 diffuses into the basic layer 53 in the form of nitrate ions NO ₃ ⁻ as shown in FIG. 7A and becomes nitrate. That is, at this time, NO _X in the exhaust gas is absorbed into the basic layer 53 in the form of nitrate.
On the other hand, FIG. 7B shows a case where the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 is made the stoichiometric air-fuel ratio or rich when NO _X is absorbed in the basic layer 53 in the form of nitrate. Is shown. In this case, since the oxygen concentration in the exhaust gas is lowered, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate absorbed in the basic layer 53 is successively converted into nitrate ions NO _3. ⁻ And released from the basic layer 53 in the form of NO ₂ as shown in FIG. 7B. Next, the released NO ₂ is reduced by the hydrocarbons HC and CO contained in the exhaust gas.
Figure 8 shows a case where NO _X absorbing capacity of the basic layer 53 is to be temporarily rich air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 shortly before saturation Yes. In the example shown in FIG. 8, the time interval of this rich control is 1 minute or more. In this case, NO _X absorbed in the basic layer 53 when the air-fuel ratio (A / F) in of the exhaust gas is lean causes the air-fuel ratio (A / F) in of the exhaust gas to be temporarily rich. When released, it is released from the basic layer 53 at once and reduced. Therefore, in this case, the basic layer 53 serves as an absorbent for temporarily absorbing NO _X.
Incidentally, at this time, sometimes the basic layer 53 temporarily adsorbs the NO _X, thus using term of storage as a term including both absorption and adsorption In this case the basic layer 53 temporarily the NO _X It plays the role of NO _X storage agent for storage. That is, in this case, if the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the exhaust purification catalyst 13 is referred to as the air-fuel ratio of the exhaust gas, the exhaust purification catalyst. 13, the air-fuel ratio of the exhaust gas is acting as _the NO _X storage catalyst during lean occludes NO _X, the oxygen concentration in the exhaust gas to release NO _X occluding the drops.
Figure 9 shows the NO _X purification rate when making the exhaust purification catalyst 13 was thus function as _the NO _X storage catalyst. The horizontal axis in FIG. 9 indicates the catalyst temperature TC of the exhaust purification catalyst 13. When the exhaust purification catalyst 13 functions as a NO _X storage catalyst, as shown in FIG. 9, when the catalyst temperature TC is 300 ° C. to 400 ° C., an extremely high NO _X purification rate is obtained, but the catalyst temperature TC is 400 ° C. NO _X purification rate decreases when a high temperature of more.
The reason why the the catalyst temperature TC becomes equal to or higher than 400 ° C. NO _X purification rate is lowered, nitrate when the catalyst temperature TC becomes equal to or higher than 400 ° C. is released from the exhaust purification catalyst 13 in the form of NO ₂ by thermal decomposition Because. That is, so long as storing NO _X in the form of nitrates, it is difficult to obtain a high NO _X purification rate when the catalyst temperature TC is high. However, in the new NO _X purification method shown in FIGS. 4 to 6A and 6B, as can be seen from FIGS. 6A and 6B, nitrate is not generated or is very small even if it is generated, and thus shown in FIG. the catalyst temperature TC is that even high NO _X purification rate is obtained when as high as.
Therefore, in the present invention, the hydrocarbon supply valve 15 for supplying hydrocarbons is disposed in the engine exhaust passage, and the hydrocarbons injected from the hydrocarbon supply valve 15 into the engine exhaust passage downstream of the hydrocarbon supply valve 15 and An exhaust purification catalyst 13 for reacting with NO _X contained in the exhaust gas is disposed. Precious metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13 and are also precious metal catalysts 51 and 52. A basic exhaust gas flow surface portion 54 is formed around the exhaust gas purification catalyst 13 so that the exhaust gas purification catalyst 13 reduces hydrocarbons from the hydrocarbon supply valve 15 to a predetermined air-fuel ratio. which has a property for reducing the NO _X which the ejecting at predetermined supply interval contained in the exhaust gas, the supply interval of a hydrocarbon to be longer than the predetermined supply interval exhaust Stored amount of NO _X contained in the vinegar has a property of increasing, so that the air-fuel ratio of the exhaust gas hydrocarbons from the hydrocarbon feed valve 15 during engine operation decreases to an air-fuel ratio to a predetermined above so that injected at a predetermined supply interval described above, thereby reducing the NO _X contained in exhaust gas in the exhaust purification catalyst 13 in.
That is, the NO _X purification methods shown in FIGS. 4 to 6A and 6B almost form nitrates when an exhaust purification catalyst carrying a noble metal catalyst and forming a basic layer capable of absorbing NO _X is used. It can be said that this is a new NO _X purification method that purifies NO _X without any problems. In fact, when this new NO _X purification method is used, the amount of nitrate detected from the basic layer 53 is extremely small compared to the case where the exhaust purification catalyst 13 functions as a NO _X storage catalyst. Incidentally, this new NO _X purification method hereinafter referred to as a first NO _X removal method.
Next, this first NO _X removal method will be described in more detail with reference to FIG 15. FIG 10.
FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG. As described above, the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 indicates the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 at the same time. In FIG. 10, ΔH indicates the amplitude of the air-fuel ratio (A / F) in, that is, the amplitude of the change in the concentration of hydrocarbon HC flowing into the exhaust purification catalyst 13, and ΔT indicates the hydrocarbon flowing into the exhaust purification catalyst 13. The concentration oscillation period, that is, the hydrocarbon supply period is shown.
Further, in FIG. 10, (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output. In other words, the base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 when the supply of hydrocarbons is stopped. On the other hand, in FIG. 10, X is the air-fuel ratio (A / F) used for the production of the reducing intermediate without the generated active NO ₂ ^* being occluded in the basic layer 53 in the form of nitrate. The upper limit of in is expressed, and in order to react active NO ₂ ^* and the reformed hydrocarbon to generate a reducing intermediate, the air-fuel ratio (A / F) in is set to be higher than the upper limit X of the air-fuel ratio. It needs to be lowered. Hereinafter, the upper limit X of the air-fuel ratio necessary for generating the reducing intermediate is referred to as a required minimum air-fuel ratio.
In the example shown in FIG. 10, the required minimum air-fuel ratio X is rich. Therefore, in this case, the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate. The following is made rich: On the other hand, in the example shown in FIG. 11, the required minimum air-fuel ratio X is lean. In this case, the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.
In this case, whether the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the exhaust purification catalyst 13. In this case, for example, if the amount of the precious metal 51 supported is increased, the exhaust purification catalyst 13 becomes stronger in oxidizing power, and if it becomes more acidic, the oxidizing power becomes stronger. Accordingly, the oxidizing power of the exhaust purification catalyst 13 varies depending on the amount of the precious metal 51 supported and the acidity.
When the exhaust purification catalyst 13 having a strong oxidizing power is used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. When the air-fuel ratio (A / F) in is lowered, the hydrocarbon is completely oxidized, and as a result, a reducing intermediate cannot be generated. On the other hand, when the exhaust purification catalyst 13 having a strong oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, the air-fuel ratio (A / F) in is rich. The hydrocarbons are partially oxidized without being completely oxidized, i.e., the hydrocarbons are reformed, thus producing a reducing intermediate. Therefore, when the exhaust purification catalyst 13 having a strong oxidizing power is used, the required minimum air-fuel ratio X needs to be made rich.
On the other hand, when the exhaust purification catalyst 13 having a weak oxidizing power is used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. In this case, the hydrocarbon is not completely oxidized but partially oxidized, that is, the hydrocarbon is reformed, and thus a reducing intermediate is produced. On the other hand, when the exhaust purification catalyst 13 having a weak oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, a large amount of hydrocarbons are not oxidized. The exhaust gas is simply exhausted from the exhaust purification catalyst 13, and the amount of hydrocarbons that are wasted is increased. Therefore, when the exhaust purification catalyst 13 having a weak oxidizing power is used, the required minimum air-fuel ratio X needs to be made lean.
That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the exhaust purification catalyst 13 becomes stronger, as shown in FIG. In this way, the required minimum air-fuel ratio X becomes lean or rich due to the oxidizing power of the exhaust purification catalyst 13, but in the case where the required minimum air-fuel ratio X is rich below, the air-fuel ratio (A / F) The amplitude ΔT of in, that is, the amplitude change ΔT of the hydrocarbon concentration flowing into the exhaust purification catalyst 13 and the oscillation period ΔT of the hydrocarbon concentration flowing into the exhaust purification catalyst 13, that is, the hydrocarbon supply cycle ΔT will be described.
When the base air-fuel ratio (A / F) b increases, that is, when the oxygen concentration in the exhaust gas before the hydrocarbons are supplied increases, the air-fuel ratio (A / F) in is made equal to or less than the required minimum air-fuel ratio X. As a result, the amount of hydrocarbons necessary for the increase increases, and the amount of excess hydrocarbons that did not contribute to the production of the reducing intermediate also increases. In this case, in order to satisfactorily purify NO _X must oxidize the excess hydrocarbons as described above, therefore in order to satisfactorily purify NO _X amounts of higher hydrocarbons the amount of the surplus is large Oxygen is needed.
In this case, the amount of oxygen can be increased by increasing the oxygen concentration in the exhaust gas. To satisfactorily purify NO _X, therefore, it is necessary to increase the oxygen concentration in the exhaust gas after the hydrocarbon feed when the oxygen concentration in the exhaust gas before the hydrocarbons are fed is high. That is, it is necessary to increase the amplitude of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.
FIG. 13 shows the relationship between the oxygen concentration in the exhaust gas before the hydrocarbon is supplied and the amplitude ΔH of the hydrocarbon concentration when the same NO _X purification rate is obtained. From FIG. 13, it can be seen that in order to obtain the same NO _x purification rate, the higher the oxygen concentration in the exhaust gas before the hydrocarbons are supplied, the more the amplitude ΔH of the hydrocarbon concentration needs to be increased. That is, it is necessary to increase the amplitude ΔT of the hydrocarbon concentration as the base air-fuel ratio (A / F) b is increased to obtain the same of the NO _X purification rate. In other words, in order to satisfactorily purify NO _X can be reduced the amplitude ΔT of the hydrocarbon concentration as the base air-fuel ratio (A / F) b becomes lower.
By the way, the base air-fuel ratio (A / F) b becomes the lowest during acceleration operation. At this time, if the amplitude ΔH of the hydrocarbon concentration is about 200 ppm, NO _X can be purified well. The base air-fuel ratio (A / F) b is usually larger than that during acceleration operation. Therefore, as shown in FIG. 14, if the hydrocarbon concentration amplitude ΔH is 200 ppm or more, a good NO _x purification rate can be obtained. become.
On the other hand, when the base air-fuel ratio (A / F) b is the highest is found that good NO _X purification rate when the amplitude ΔH of the hydrocarbon concentration of about 10000ppm is obtained. Therefore, in the present invention, the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm.
Further, when the vibration period ΔT of the hydrocarbon concentration becomes longer, the oxygen concentration around the active NO ₂ ^* becomes higher while the hydrocarbon is supplied after the hydrocarbon is supplied. In this case, when the vibration period ΔT of the hydrocarbon concentration becomes longer than about 5 seconds, the active NO ₂ ^* begins to be absorbed in the basic layer 53 in the form of nitrate, and therefore the vibration of the hydrocarbon concentration as shown in FIG. When the period ΔT becomes longer than about 5 seconds NO _X purification rate falls. Therefore, the oscillation period of the hydrocarbon concentration, that is, the hydrocarbon supply period ΔT needs to be 5 seconds or less.
On the other hand, when the vibration period ΔT of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon starts to accumulate on the exhaust gas flow surface of the exhaust purification catalyst 13, and therefore, as shown in FIG. NO _X purification rate decreases the vibration period ΔT approximately 0.3 seconds becomes below. Therefore, in the present invention, the oscillation cycle of the hydrocarbon concentration, that is, the hydrocarbon supply cycle is set to be between 0.3 seconds and 5 seconds.
Now, lowering the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 as described above until the required minimum air-fuel ratio X in order to purify the NO _X using the first NO _X removal method It is necessary to let In the embodiment according to the present invention, the hydrocarbon supply amount W that can reduce the air-fuel ratio (A / F) in of the exhaust gas to the required minimum air-fuel ratio is a function of the injection amount Q from the fuel injection valve 3 and the engine speed N. Is stored in advance in the ROM 32 in the form of a map as shown in FIG.
On the other hand, FIG. 16B shows the reducing intermediate holding time during which the reducing intermediate generated on the basic layer 53 of the exhaust purification catalyst 13 can be held. When the temperature TC of the exhaust purification catalyst 13 rises, this reducing intermediate is easily detached from the basic layer 53. Therefore, as shown in FIG. 16B, the reducing intermediate is retained as the temperature TC of the exhaust purification catalyst 13 increases. Time will be shorter. By the way, when the hydrocarbon supply period ΔT becomes longer than the reducing intermediate retention time, a period in which the reducing intermediate does not exist occurs, and the NO _x purification rate decreases. In order to prevent such a period in which the reducing intermediate does not exist, it is necessary to make the hydrocarbon feed period ΔT equal to the reducing intermediate holding time or shorter than the reducing intermediate holding time. There is. Therefore, in the embodiment according to the present invention, the hydrocarbon supply period ΔT is shortened as the temperature TC of the exhaust purification catalyst 13 increases. This hydrocarbon supply cycle ΔT is also stored in advance in the ROM 32 in the form of a map as shown in FIG. 16C as a function of the injection amount Q and the engine speed N.
Next will be specifically described NO _X purification method when the exhaust purification catalyst 13 with reference made to function as the NO _X storing catalyst to FIGS. 17 to 20. Hereinafter, the NO _X purification method in the case where the exhaust purification catalyst 13 functions as the NO _X storage catalyst is referred to as a second NO _X purification method.
In this second NO _X purification method, as shown in FIG. 17, the exhaust flowing into the exhaust purification catalyst 13 when the stored NO _X amount ΣNOX stored in the basic layer 53 exceeds a predetermined allowable amount MAX. The air-fuel ratio (A / F) in of the gas is temporarily made rich. When the air-fuel ratio (A / F) in of the exhaust gas is made rich, NO _X occluded in the basic layer 53 from the basic layer 53 when the air-fuel ratio (A / F) in of the exhaust gas is lean. It is released at once and reduced. Thereby, NO _X is purified.
Occluded amount of NO _X ΣNOX is calculated from the amount of NO _X discharged from the engine, for example. In the embodiment according to the present invention is stored in advance in the ROM32 in the form of a map as shown in FIG. 18 as a function of the discharge amount of NO _X NOXA the injection quantity Q and the engine speed N which is discharged from the engine per unit time, The stored NO _X amount ΣNOX is calculated from this exhausted NO _X amount NOXA. In this case, as described above, the period during which the air-fuel ratio (A / F) in of the exhaust gas is made rich is usually 1 minute or more.
In this second NO _X purification method, as shown in FIG. 19, the exhaust gas flowing into the exhaust purification catalyst 13 by injecting the additional fuel WR into the combustion chamber 2 from the fuel injection valve 3 in addition to the combustion fuel Q. The air / fuel ratio (A / F) in of the gas is made rich. The horizontal axis in FIG. 19 indicates the crank angle. This additional fuel WR is injected when it burns but does not appear as engine output, that is, slightly before ATDC 60 ° after compression top dead center. This fuel amount WR is stored in advance in the ROM 32 as a function of the injection amount Q and the engine speed N in the form of a map as shown in FIG. Of course, the air-fuel ratio (A / F) in of the exhaust gas can be made rich by increasing the amount of hydrocarbons supplied from the hydrocarbon supply valve 15 in this case.
Now, lowering the air-fuel ratio (A / F) in of the exhaust gas to purify the NO _X using the first NO _X removal method is to flow into the exhaust purification catalyst 13 to the required minimum air-fuel ratio X as described above It is necessary to let In this case, in the embodiment described so far, the air-fuel ratio (A / F) in of the exhaust gas is lowered to the required minimum air-fuel ratio X by the hydrocarbon W supplied from the hydrocarbon supply valve 15. A method of supplying hydrocarbon W from only the hydrocarbon supply valve 15 to reduce the air-fuel ratio (A / F) in of the exhaust gas to the required minimum air-fuel ratio X is hereinafter referred to as a first hydrocarbon supply method. Called. The change in the air-fuel ratio (A / F) in by this first hydrocarbon supply method is schematically shown in FIG. 21A.
On the other hand, when the fuel is injected from the fuel injection valve 3 into the combustion chamber 2 during the latter half of the expansion stroke or the exhaust stroke after 70 ° after compression top dead center, that is, after the combustion of the combustion fuel is completed, the fuel is injected. This fuel is then cracked without creating a flame and burning it. That is, the fuel is reformed to a hydrocarbon having a small carbon number. The injection performed after the combustion of the combustion fuel is referred to as post (rear) injection.
A hydrocarbon supply method using this post-injection is schematically shown as a second hydrocarbon supply method in FIG. 21A. As shown in FIG. 21A, in the second hydrocarbon supply method, the air-fuel ratio (A / F) of the exhaust gas flowing into the exhaust purification catalyst 13 by the supply hydrocarbon WA from the hydrocarbon supply valve 15 and the supply fuel WB by post-injection. F) in is the required minimum air-fuel ratio X. The supplied fuel WB by the post injection is shown in FIG. 21B similar to FIG. In the embodiment according to the present invention, this post injection is performed between 70 ° and 150 ° after the compression top dead center indicated by the range θ in FIG. 21B.
In the first hydrocarbon supply method, most of the hydrocarbon W supplied from the hydrocarbon supply valve 15 is used to consume oxygen, that is, to reduce the air-fuel ratio (A / F) in. And only a part of the hydrocarbon W fed from the hydrocarbon feed valve 15 is used for the production of the reducing intermediate. That is, the amount of hydrocarbon used for the production of the reducing intermediate is extremely small.
Therefore, in the second hydrocarbon supply method, only the hydrocarbon amount WA required for the production of the reducing intermediate is supplied from the hydrocarbon supply valve 15, oxygen is consumed by the supplied fuel WB by post injection, and the air-fuel ratio (A / F ) In is lowered. Although the fuel WB supplied by post injection is also a hydrocarbon, this hydrocarbon is completely oxidized and disappears because it is reformed into a hydrocarbon having a small carbon number. Therefore, no reducing intermediate is produced from the supplied fuel WB, and the reducing intermediate is produced by the hydrocarbon WA that is partially oxidized.
By the way, since the reducing intermediate is produced from one NO _X and one radical hydrocarbon, theoretically, if the amount (mol) of radical hydrocarbon is the same as the amount of NO _X (mol), all NO NO _X can be reduced. However, in order to reduce all NO _X , radical hydrocarbons are actually required several times as much as NO _X. Therefore the supply amount WA of hydrocarbons into account that this is in the embodiment according to the present invention increases as _the amount of NO _X to be reduced as shown in FIG. 22A, that is, _the amount of NO _X NOXA exhausted from the engine increases To be harassed.
That is, in the embodiment according to the present invention, when the second hydrocarbon supply method is used, the hydrocarbon supply amount WA supplied from the hydrocarbon supply valve 15 is the NO in the exhaust gas flowing into the exhaust purification catalyst 13. It is determined according to the amount of _X.
Here, the NO _X amount NOXA discharged from the engine is a function of the injection amount Q and the engine speed N as shown in FIG. 18, and the hydrocarbon supply amount WA is also a function of the injection amount Q and the engine speed N. Become. Therefore, in the embodiment according to the present invention, this hydrocarbon supply amount WA is stored in advance in the ROM 32 in the form of a map as shown in FIG. 22B as a function of the injection amount Q and the engine speed N.
On the other hand, when the injection amount Q and the engine speed N are determined, the base air-fuel ratio (A / F) b is determined, the required minimum air-fuel ratio X is determined, and the hydrocarbon supply amount WA is determined. Accordingly, as can be seen from FIG. 21A, the fuel supply amount WB by post injection is also determined at this time. Accordingly, in the embodiment according to the present invention, the supplied fuel amount WB by the post injection is also stored in advance in the ROM 32 in the form of a map as shown in FIG. 22C as a function of the injection amount Q and the engine speed N.
FIG. 23 and FIG. 24 show specific examples of the second hydrocarbon supply control.
In the example shown in FIG. 23, the fuel WB is supplied by post injection in several consecutive expansion strokes from just before the hydrocarbon WA is supplied from the hydrocarbon supply valve 15 to immediately after the hydrocarbon WA is supplied. Shows the case. In this case, the air-fuel ratio (A / F) in is lowered by supplying the fuel WB by post injection, and the air-fuel ratio (A / F) in is reduced to the required minimum air-fuel ratio by supplying the hydrocarbons WA. It is lowered to X.
On the other hand, in the example shown in FIG. 24, when the second hydrocarbon supply control is started, fuel WB is supplied by post-injection every expansion stroke. Therefore, in this example, when the second hydrocarbon supply control is started, the air-fuel ratio (A / F) in is continuously decreased, and when the hydrocarbon WA is supplied, the air-fuel ratio (A / F) in is decreased. The required minimum air-fuel ratio X is lowered.
By the way, since the fuel supplied by post injection is cracked, it easily reacts with oxygen. Therefore, when fuel is supplied by post injection, oxygen can be consumed more easily than when hydrocarbon is supplied from the hydrocarbon supply valve 15. There is an advantage. On the other hand, when post injection is used, both post injection and hydrocarbon WA supply control must be performed.
Accordingly, in the present invention, in consideration of these matters, the hydrocarbon W from the hydrocarbon feed valve 15 is reduced in advance so that the air-fuel ratio (A / F) in of the exhaust gas decreases to a predetermined air-fuel ratio X during engine operation. A first hydrocarbon supply method for purifying NO _x contained in the exhaust gas by injecting at a predetermined supply interval ΔT, and reducing the supply amount of hydrocarbons from the hydrocarbon supply valve 15 and exhausting the exhaust gas; Selection is made between the fuel ratio (A / F) in and the second hydrocarbon supply method for supplying the fuel WB necessary for lowering to a predetermined air-fuel ratio X into the combustion chamber 2 during the latter half of the expansion stroke or during the exhaust stroke. Used.
On the other hand, as described above, the post-injection fuel WB is more likely to be oxidized than the hydrocarbon WA, and therefore, when the post-injection fuel WB is supplied, the oxidation reaction is higher than when only the hydrocarbon WA is supplied. Heat is obtained. Therefore, in the embodiment according to the present invention, the second hydrocarbon supply method is used when the temperature of the exhaust treatment device such as the exhaust purification catalyst 13 or the particulate filter 14 is raised.
FIG. 25A shows the temperature rise control of the exhaust purification catalyst 13. For example reduces the engine load at the time of engine operation, the temperature TC is lower than the activation temperature TC ₀ predetermined when NO _X purification rate of the exhaust purification catalyst 13 an exhaust temperature is reduced is reduced. Therefore, as shown in FIG. 25A, when the temperature TC of the exhaust purification catalyst 13 is higher than the activation temperature TC ₀ , the first hydrocarbon supply method is used, and the temperature TC of the exhaust purification catalyst 13 becomes the activation temperature TC. _{When the} temperature falls below ₀ , the second hydrocarbon supply method is used to raise the temperature of the exhaust purification catalyst 13.
That is, in the embodiment shown in FIG. 25A, when the temperature TC of the exhaust purification catalyst 13 falls below a predetermined activation temperature TC ₀ , the first hydrocarbon supply method is switched to the second hydrocarbon supply method. Thus, the temperature raising action of the exhaust purification catalyst 13 is performed.
FIG. 25B shows the temperature rise control of the particulate filter 14. In order to regenerate the particulate filter 14 by burning the particulates deposited on the particulate filter 14, the temperature TD of the particulate filter 14 must be raised to a regeneration temperature TX of 600 ° C. or higher. Therefore, in the embodiment shown in FIG. 25B, when the particulate filter 14 is to be regenerated, the first hydrocarbon supply method is switched to the second hydrocarbon supply method, whereby the temperature raising action of the particulate filter 14 is performed. . In this embodiment, when the temperature TD of the particulate filter 14 exceeds the regeneration temperature TX, a small amount of post-injection fuel WB continues to be supplied to maintain the temperature TD of the particulate filter 14 at or above the regeneration temperature TX.
Next, the operation control method according to the present invention will be described.
Figure 26 is NO in the exhaust purification catalyst 13 when the NO _X purification rate when the purification process of the NO _X is being performed, the second NO _X removal method has been used by the first NO _X removal method _X storage rate is shown. In the present invention, when the NO _X purification rate is higher than the NO _X storage rate, that is, when the temperature TC of the exhaust purification catalyst 13 is relatively high, the first NO _X purification method is used, and the NO _X storage rate is the NO _X purification rate. Is higher, that is, when the temperature TC of the exhaust purification catalyst 13 is low, the second NO _X purification method is used. At the time of engine startup therefore usually used are second NO _X removal method, it is switched when the temperature TC of the exhaust purification catalyst 13 becomes higher from the second NO _X removal method to the first NO _X removal method.
On the other hand, in the present invention, when the second hydrocarbon supply control is performed under the first NO _X purification method, the air-fuel ratio (A / F) in of the exhaust gas is reliably reduced to the required minimum air-fuel ratio X. Thus, the fuel amount WB by post injection is feedback controlled. In order to perform this feedback control, it is necessary to detect the actual minimum air-fuel ratio when the second hydrocarbon supply method is used.
FIG. 27 shows a routine for detecting this actual minimum air-fuel ratio. This routine is executed by interruption at regular intervals only during the air-fuel ratio detection period shown in FIGS.
Referring to FIG. 27, first, the air-fuel ratio (A / F) n of the exhaust gas detected by the air-fuel ratio sensor 26 in step 60 is read. Next, at step 61, the air-fuel ratio (A / F) in that has become minimum within the air-fuel ratio detection period is detected. Next, at step 62, it is judged if the air-fuel ratio detection period has elapsed. When the air-fuel ratio detection period has elapsed, the routine proceeds to step 63 where the minimum air-fuel ratio (A / F) n is reduced to the minimum air-fuel ratio (A / F). F) t.
FIG. 28 and FIG. 29 show an engine operation control routine, which is also executed by interruption every predetermined time.
Referring to FIG. 28, first, at step 70, it is judged if a selection flag indicating that the first NO _X purification method should be selected is set. And NO _X purification rate is second NO _X removal method used when the purification process of the NO _X is performed by the first NO _X removal method proceeds to step 71 when the selection flag is not set It is determined whether or not the NO _X storage rate in the exhaust purification catalyst 13 at that time is higher. When the NO _X purification rate is lower than the NO _X storage rate, the routine proceeds to step 72 in FIG. 29, where the second NO _X purification method is executed.
That is, the discharge amount of NO _X NOXA per unit time is calculated from the map shown in step 72 in FIG. 18. Then occluded amount of NO _X ΣNOX is calculated by adding the discharge amount of NO _X NOXA to ΣNOX step 73. Next, at step 74 occluded amount of NO _X ΣNOX whether exceeds the allowable value MAX or not. When ΣNOX> MAX, the routine proceeds to step 75 where the additional fuel amount WR is calculated from the map shown in FIG. 20 and the additional fuel injection action is performed. Next, at step 76, ΣNOX is cleared.
On the other hand, when it is determined in step 71 of FIG. 71 that the NO _X purification rate is higher than the NO _X storage rate, the routine proceeds to step 77, where the selection flag is set, and then the routine proceeds to step 78. Once the selection flag is set, the routine jumps from step 70 to step 78. In step 78, it is determined whether or not a temperature increase flag I indicating that the temperature increase control of the exhaust purification catalyst 13 shown in FIG. 25A should be performed is set. When the temperature raising flag I is not set, the routine proceeds to step 79.
Temperature TC of the exhaust purification catalyst 13 detected by the temperature sensor 23 in step 79 it is determined whether or not the drops below the activation temperature TC _0. When TC ≧ TC _0, the routine proceeds to step 80, where it is judged if the temperature raising flag II indicating that the temperature raising control of the particulate filter 14 shown in FIG. 25B should be performed is set. When the temperature increase flag II is not set, the routine proceeds to step 81 where it is judged if the differential pressure ΔP across the particulate filter 14 detected by the differential pressure sensor 24 has become higher than the allowable value PX. When ΔP ≦ PX, the routine proceeds to step 82 in FIG. 29, where hydrocarbons are supplied by the first hydrocarbon supply method.
That is, in step 82, the hydrocarbon supply amount W is calculated from the map shown in FIG. 16A, and then in step 83, the hydrocarbon supply period ΔT is calculated from the map shown in FIG. 16C. Next, at step 84, hydrocarbon supply control is performed in which the supply amount W of hydrocarbons is supplied from the hydrocarbon supply valve 15 with the supply period ΔT.
On the other hand, if it is determined in step 79 of FIG. 28 that TC <TC ₀ , the routine proceeds to step 85 where the temperature raising flag I is set and the processing cycle is completed. Once the temperature raising flag I is set, the processing cycle is completed through step 78 thereafter. That is, when the temperature raising flag I is set, the hydrocarbon supply control by the first hydrocarbon supply method is stopped. At this time, the temperature raising control of the exhaust purification catalyst 13 is performed in the time interruption routine shown in FIG.
If it is determined in step 81 in FIG. 28 that ΔP> PX, the routine proceeds to step 86 where the temperature raising flag II is set and the processing cycle is completed. Once the temperature raising flag II is set, the processing cycle is completed through step 80 thereafter. That is, when the temperature raising flag II is set, hydrocarbon supply control by the first hydrocarbon supply method is stopped. At this time, the temperature raising control of the particulate filter 14 is performed in the time interruption routine shown in FIG.
Referring to the time interruption routine shown in FIG. 30, first, at step 90, it is judged if the temperature raising flag I is set. When the temperature raising flag I is set, the routine proceeds to step 91, where exhaust purification is performed. It is determined whether or not the temperature TC of the catalyst 13 is higher than a temperature (TC ₀ + α) obtained by adding a constant value α to the activation temperature TC ₀ . When TC ≦ TC ₀ + α, the routine proceeds to step 92 where the temperature raising control of the exhaust purification catalyst 13 shown in FIG. 25A is performed.
That is, first, at step 92, the hydrocarbon supply amount WA is calculated from the map shown in FIG. 22B, and then at step 93, the supply fuel amount WB by post injection is calculated from the map shown in FIG. 22C. Next, at step 94, it is judged if the detection of the minimum air-fuel ratio (A / F) t by the routine shown in FIG. 27 is completed. When it is first determined that the minimum air-fuel ratio (A / F) t has been detected, the routine proceeds to step 95 and then jumps to step 98.
In step 95, it is determined whether or not the detected minimum air-fuel ratio (A / F) t is lower than an air-fuel ratio (X-β) obtained by subtracting a fixed value β from the required minimum air-fuel ratio X. When (A / F) t ≧ X−β, that is, when the detected minimum air-fuel ratio (A / F) t has not decreased to the air-fuel ratio (X-β), the routine proceeds to step 97 where the fuel supply amount WB is increased. A fixed value ΔK is added to the correction value ΔWB. Next, the routine proceeds to step 98. On the other hand, when it is determined at step 95 that (A / F) t <X−β, the routine proceeds to step 96 where the constant value ΔK is subtracted from the correction value ΔWB, and then the routine proceeds to step 98.
In step 98, a correction value ΔWB is calculated for the fuel supply amount WB. Next, at step 99, the hydrocarbon of the supply amount WA is supplied from the hydrocarbon supply valve 15 with the supply cycle ΔT calculated from the map shown in FIG. 16C, and as shown in FIG. From the front, fuel of the fuel amount WB is supplied into the combustion chamber 2 by post injection. On the other hand, when it is determined at step 91 that TC> TC ₀ + α, the routine proceeds to step 100 where the temperature raising flag I is reset.
Next, referring to the time interruption routine shown in FIG. 31, first, at step 110, it is judged if the temperature raising flag II is set. When the temperature raising flag II is set, the routine proceeds to step 111. It is determined whether or not the temperature TD of the particulate filter 14 has become higher than the regeneration temperature TX. When TD ≦ TX, the routine proceeds to step 112 where the temperature rise control of the particulate filter 14 shown in FIG. 25B is performed.
That is, first, at step 112, the hydrocarbon supply amount WA is calculated from the map shown in FIG. 22B, and then at step 113, the supply fuel amount WB by post injection is calculated from the map shown in FIG. 22C. Next, at step 114, it is judged if the detection of the minimum air-fuel ratio (A / F) t by the routine shown in FIG. 27 is completed. When it is first determined that the minimum air-fuel ratio (A / F) t has been detected, the routine proceeds to step 115 and then jumps to step 118.
In step 115, it is determined whether or not the detected minimum air-fuel ratio (A / F) t is lower than an air-fuel ratio (X-β) obtained by subtracting a fixed value β from the required minimum air-fuel ratio X. When (A / F) t ≧ X−β, the routine proceeds to step 117, where the constant value ΔK is added to the correction value ΔWB for the fuel supply amount WB. Next, the routine proceeds to step 118. On the other hand, when it is determined at step 115 that (A / F) t <X−β, the routine proceeds to step 116 where the constant value ΔK is subtracted from the correction value ΔWB, and then the routine proceeds to step 118.
In step 118, a correction value ΔWB is calculated for the fuel supply amount WB. Next, at step 119, the hydrocarbon of the supply amount WA is supplied from the hydrocarbon supply valve 15 with the supply cycle ΔT calculated from the map shown in FIG. 16C, and as shown in FIG. From the front, fuel of the fuel amount WB is supplied into the combustion chamber 2 by post injection.
On the other hand, if it is determined in step 111 that TD> TX, the routine proceeds to step 120 where post-injection is performed as shown in FIG. 25B to maintain the temperature TD of the particulate filter 14 at or above the regeneration temperature TX. Control is performed. Next, at step 121, it is determined whether or not the regeneration process has been completed. When it is determined that the regeneration process has been completed, the routine proceeds to step 122, where the temperature raising flag II is reset.
As another embodiment, an oxidation catalyst for reforming hydrocarbons may be disposed in the engine exhaust passage upstream of the exhaust purification catalyst 13.

4 ... Intake manifold 5 ... Exhaust manifold 7 ... Exhaust turbocharger 12 ... Exhaust pipe 13 ... Exhaust purification catalyst 14 ... Particulate filter 15 ... Hydrocarbon supply valve

Claims (9)

A hydrocarbon supply valve for supplying hydrocarbons is disposed in the engine exhaust passage, and the hydrocarbons injected from the hydrocarbon supply valve into the engine exhaust passage downstream of the hydrocarbon supply valve and NO _X contained in the exhaust gas An exhaust purification catalyst is made to react with the noble metal catalyst, a noble metal catalyst is supported on the exhaust gas circulation surface of the exhaust purification catalyst, and a basic exhaust gas circulation surface portion is formed around the noble metal catalyst. The exhaust purification catalyst is configured to be configured so that NO is contained in the exhaust gas when the hydrocarbon is injected from the hydrocarbon supply valve at a predetermined supply interval so that the air-fuel ratio of the exhaust gas decreases to a predetermined air-fuel ratio. which has a property for reducing the _X, the feed interval of the hydrocarbons have the property of absorbing the amount of NO _X contained in the exhaust gas to be longer than the supply interval defined the advance is increased, the engine operating The air-fuel ratio of the exhaust gas hydrocarbons from the hydrocarbon feed valve to purify NO _X contained injected to the exhaust gas at the predetermined supply interval to drop to the air-fuel ratio of said predetermined on No. 1 hydrocarbon supply method and the fuel required to reduce the amount of hydrocarbons supplied from the hydrocarbon supply valve and reduce the air-fuel ratio of the exhaust gas to the predetermined air-fuel ratio in the latter half of the expansion stroke or exhaust An exhaust gas purification apparatus for an internal combustion engine, which selectively uses a second hydrocarbon supply method for supplying into a combustion chamber during a stroke.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the second hydrocarbon supply method is used when the temperature of the exhaust treatment apparatus is raised.   When the exhaust treatment device comprises the exhaust purification catalyst, and the temperature of the exhaust purification catalyst falls below a predetermined activation temperature, the first hydrocarbon supply method is switched to the second hydrocarbon supply method. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the temperature raising action of the exhaust gas purification catalyst is performed.   The exhaust gas purification device comprises a particulate filter disposed in the engine exhaust passage, and when the particulate filter is to be regenerated, the first hydrocarbon supply method is switched to the second hydrocarbon supply method, and the particulate filter The exhaust emission control device for an internal combustion engine according to claim 2, wherein the temperature raising action is performed. In the exhaust purification catalyst, NO _X contained in the exhaust gas reacts with the reformed hydrocarbon to produce a reducing intermediate containing nitrogen and hydrocarbon, and a predetermined supply cycle of the hydrocarbon The exhaust purification device for an internal combustion engine according to claim 1, wherein is a supply cycle necessary for continuing to generate the reducing intermediate.   6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the hydrocarbon supply cycle is between 0.3 seconds and 5 seconds.   The exhaust purification device for an internal combustion engine according to claim 1, wherein the noble metal catalyst is composed of platinum Pt and at least one of rhodium Rh and palladium Pd. The basic layer comprising a metal which can donate electrons to the alkali metal or alkaline earth metal or rare earth or NO _X in the exhaust gas flow on the surface of the exhaust purification catalyst is formed, the surface of the base layer is the base The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas circulation surface portion is formed. The amount of hydrocarbons supplied from the hydrocarbon supply valve when the second hydrocarbon supply method is used is determined according to the amount of NO _{x in} the exhaust gas flowing into the exhaust purification catalyst. 2. An exhaust emission control device for an internal combustion engine according to 1.

Images